The present invention relates to a method and an apparatus for fabricating a spinde housing with a ball bearing and, more particularly, relates to a method and an apparatus for fabricating a spindle housing with a ball bearing so as to eliminate variations in the built-in breadth of a molded plastic housing with a ball bearing.
FIG. 4 shows the conventional spindle assembly which is incorporated as a spindle assembly for a floppy disk of an office automation (OA) equipment. In FIG. 4, numeral 10 designates a spindle housing made of synthetic resin and fixed on a base plate 11. A cup 15 is rotatably supported by two ball bearings 13 and 14 mounted in a cylinder 12 of the spindle housing 10. The cup 15 is coupled to a holder 16 with a screw 17. The spindle housing 10 is formed directly on the ball bearing 14 by fabricating. The other ball bearing 13 is mounted in a cylinder 12 of the spindle housing 10 after a molding operation. A laminated spring 19 is interposed between an inwardly-directed flange 18 of the cylinder 12 and an outer race of the ball bearing 13. The elastic force of the spring 19 affords a pre-load to the ball bearings 13 and 14 to eliminate internal clearances of the ball bearings 13 and 14.
In the above-structured spindle assembly, conventionally, it is necessary that the variations in an axial distance L between an edge (a) of a fixing portion 20 of the housing 10 and an upper face (b) of the cup 15 are limited within a predetermined allowance, so that the relative positioning of a floppy disk 21 and a head 22 (both shown in dashed lines) is controlled. The variations in the built-up breadth (L) are equal to the sum of the respective variations in an axial distance (c) of the housing 10, an assembled breadth (d) of the ball bearing 14, and an axial distance (e) of the cup 15.
Since the cup 15 is normally made of aluminum, numerically controlled machining can be applied to it to make the variations in the distance (e) of the cup 15 extremely small. Also, the housing 10 having little variations in the distance (c) can be obtained because the housing 10 is molded. On the contrary, the ball bearing 14 has radial clearance, race curvature ratio of the inner and the outer races, the diameter of the ball, and the deflection of the raceway track as a variety of reasons for the variations. The variations in the assembled breadth (d) of the ball bearing 14 might exceed the total allowance of the variations in the built-up breadth (L) of the spindle assembly. Owing to the main reason of the variations of the assembled breadth (d) of the ball bearing 14, the variation in the built-up breadth (L) of the spindle assembly cannot be limited within the total allowance of the variations by conventional molding and assembling.
Therefore, conventionally, after assembly, the edge (b) of the cup 15 is finished with machining, so that the variations in the built-up breadth (L) of the spindle assembly are limited within the total allowance of the variations; however, this operating is troublesome. Particular machining equipment must be provided.